To determine the alternate pathways of bilirubin metabolism by isolation of bilirubin derivatives excreted in the bile and/or urine of: a. Newborn infants undergoing phototherapy for neonatal jaundice. b. Subjects with unstable hemoglobinopathies and Heinz-body formation. A. To elucidate the mechanism by which phototherapy accelerates the turnover of bile acids in patients with stable cholestatic jaundice due to alcoholic cirrhosis. The concentrations and specific activities of serum and urine bile acids will be determined in such patients, and compared with the concentrations and specific activities on the comparable bile acids in bile. Bile acids will be isolated by absorption to XAD-2 gel (Paumgartner). Similar studies will be performed in subjects without liver disease. The possibility of two bile acid pools in cholestasis will be assessed by simultaneous measurement of turnover of C14 and H3-cholic acid, one given i.v. and the other intraduodenally. B. The effect of phototherapy on hepatic drug metabolizing enzymes and cytochrome P450 concentrations will be determined in normal and Gunn rats. To elucidate the mechanism of formation of pigment gallstones: a. The insoluble black pigment will be degraded to its monopyrrolic components by the Rudiger chromic oxidation technique, and the fragments identified by chemical and mass spectrometric analysis. b. The effect of various bile constituents on the solubility of unconjugated bilirubin will be determined in model systems. c. The composition of the two types of pigment gallstones we have detected will be determined, and compared in cirrhotic and non-cirrhotic subjects.